This invention generally relates to dilatation balloons which are used on balloon dilatation catheters for percutaneous transluminal coronary angioplasty (PTCA).
In conventional PTCA procedures, a guiding catheter having a preshaped distal tip is percutaneously introduced into the cardiovascular system of a patient and advanced therein until the preshaped distal tip of the guiding catheter is disposed within the aorta adjacent the ostium of the desired coronary artery. The guiding catheter is twisted or torqued from the proximal end to turn the distal tip of the guiding catheter so that it can be guided into the coronary ostium. With over the wire dilatation catheter systems, a guidewire and a balloon dilatation catheter are introduced into and advanced through the guiding catheter to the distal tip, with the guidewire slidably disposed within an inner lumen of the dilatation catheter. The guidewire is first advanced out the distal tip of the guiding catheter, which is seated in the ostium of the patient's coronary artery, until the distal end of the guidewire crosses the lesion to be dilated. The dilatation catheter is then advanced out of the distal tip of the guiding catheter, over the previously advanced guidewire, until the balloon on the distal extremity of the dilatation catheter is properly positioned across the lesion. The balloon is then inflated to a predetermined size with radiopaque liquid at relatively high pressures (e.g., generally 4-12 atmospheres) to dilate the stenosed region of the diseased artery. After one or more inflation-deflation cycles, the balloon is finally deflated so that the dilatation catheter can be removed from the dilated stenosis and blood flow will resume through the artery.
A continual effort has been made by those skilled in the art to reduce the profile, i.e. transverse dimensions, of dilatation catheters, particularly the balloon, to enable the catheter to be advanced much further into a patient's vasculature or other body lumens and to cross much tighter or narrower lesions. In the case of balloons for prostatic urethral dilatations the reduced deflated profile of the balloon is also important to facilitate advancing and withdrawing the balloon through a conventional cystoscope.
The prior art dilatation balloons for dilatation catheters have generally been formed of relatively inelastic polymeric materials such as polyethylene, polyvinyl chloride, polyethylene terephthalate (PET) and polyolefinic ionomers. The dilatation balloons made of these materials were frequently heat formed in the deflated state so as to wrap around an inner member within the catheter in order to present as low a profile as possible. However, when the prior art balloons are deflated after being inflated, they have a tendency to form outwardly projecting wings which can interfere with the passage the deflated balloons through body lumens and particularly the stenosis to be dilatated. This is particularly true of balloons made of high strength plastic materials such as PET and Nylon. However, high strength balloon materials are preferred because these balloons can be made with much thinner walls and therefore allow for much lower profiles than balloons formed of lower strength materials. Additionally, the tapered section of the balloon for dilatation catheters generally is much thicker and therefore less flexible than the working section of the balloon. As a result the thicker section is less apt to collapse upon deflation than the working section, thereby providing a larger profile.
What has been needed and heretofore unavailable is a dilatation balloon formed of high strength polymer materials which upon deflation after inflation returns to a very low profile along the entire length of the balloon. The present invention satisfies this and other needs.